Using Sabermetrics for Fantasy Baseball: Ballpark Factors

If you have ever selected a streamable pitcher based on home park or benched an otherwise must-start arm at Coors Field, you already know how much a stadium can impact a player's bottom line.

Ballpark Factors quantify the influence each stadium has, allowing you to make the most of your fantasy team's real-life schedule. However, the math involved is approximate, and random fluctuations in weather patterns and sheer dumb luck can make the same parks play very differently year to year.

Today, we continue our journey through baseball sabermetrics with a look at how each team's home stadium can play a factor in the fantasy baseball world.

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How to Interpret Ballpark Factors

Ballpark factors are generally set to a base of 100 (or 1.000, which doesn't actually change anything), meaning that a park factor of 100 plays perfectly neutral. Factors greater than 100 signify that a given park allows more of that outcome, while numbers below 100 represent less of those outcomes.

There are multiple sources of ballpark factors, including FanGraphs, Baseball Prospectus, ESPN, and Statcorner. Each calculates its numbers a little bit differently, but they all use the base-100 scale listed above. There is no "correct" factor to use, as each system has its own merits. Just make sure you stick to a single source for any analysis to control for the variance.

The source you choose also dictates how much each point above or below 100 is "worth." A player only plays 50% of his games at home, with the rest of his schedule comprised of road games. Some sources such as Fangraphs halve all of their factors to accommodate this, making each point above or below 100 represent a one percent increase or decrease over a full season of stats. Other sources leave that job to you, making every point worth two percentage points in a player's final line.

If that's too confusing, it's fine to forget it. The only thing you need to know is that a park factor of 110 is considerably higher than a 105 mark. It's also important to note that ballpark factors aren't everything. If a particular park has a runs factor of 99, that isn't a strong enough argument to stream a pitcher there absent other compelling reasons.

When most fantasy owners think of ballpark factors, they think of homers. A park allowing plenty of bombs is viewed as a hitter's park, while parks allowing fewer dingers are more pitcher-friendly. Let's consider Guaranteed Rate Field as an example.

The home of the Chicago White Sox is known as a home run haven for good reason. In 2019, the stadium had a Baseball Prospectus HR factor of 106 for right-handed batters and 125 for left-handed swingers. This means that the stadium helps left-handed hitters more than right-handed hitters, creating a meaningful platoon split in how the park plays. Of course, a right-handed hitter with an opposite-field power stroke could benefit like a lefty, and a HR factor of 106 is nothing to sneeze at. The point is that all ballpark factors should be considered with nuance.

While most fantasy managers are familiar with certain ballparks allowing more or fewer homers than others, BABIP is an under-appreciated component of ballpark factors. Altitude, infield conditions, foul territory, batter's eye, and the size of the stadium can all influence how a ballpark plays beyond just home runs.

Coors Canaveral

For example, the Colorado Rockies managed a league-leading .348 BABIP at home in 2019 against a  road BABIP of .292 that ranked second to last. The Rockies have a similar split in every year of their existence, so 2019 was no fluke. Players tend to perform a little better at home, but Colorado's splits seem indicative of more than that.

Indeed, Coors Field promoted more singles (111 for RHB, 108 for LHB per Baseball Prospectus), doubles (121, 104), triples (193, 120), and homers (109, 109) than the average park in 2019. The sample size of triples is usually too small to mean anything, but Coors Field has many quirks to help explain its extreme offensive environment.

It's a gigantic ballpark, offering plenty of real estate for balls to find grass. Breaking balls behave differently due to the elevation of the Mile High City, removing some pitching weapons. Fatigue may set in faster for the same reason. The introduction of the humidor has decreased the ballpark's HR rates compared to the complete bandbox it was at the height of the Steroid Era, but it still consistently posts the highest BABIPs in baseball. For this reason, fantasy gamers should generally be skeptical of Colorado hurlers.

Colorado is the most extreme example, but every stadium has some quirk that makes it unique. Fenway's Green Monster, the Trop's artificial surface, and the miles of foul territory in Oakland can all affect a player's fantasy stats.

That said, sometimes ballpark factors can lie. Eighty-one games are a relatively small sample size, so a park could play dramatically differently in a given season than it has in the past or should be expected to moving forward. Some ballpark factors come in three-season or five-season variants to attempt to filter out some of this noise, but it's still something to consider in your analysis.

Conclusion

Ballpark factors quantify how much influence a player's environment has on his final totals. A 100 factor is league-average, with numbers above or below that indicative of more or less of whatever it is a factor for. Most fantasy owners think of homers when considering park factors, but singles, line drives, and even strikeouts have park factors as well. Platoon splits can also dictate where a given player is most likely to succeed. Check out this link for more information on how to use advanced metrics to dominate your leagues.